This invention relates to vehicle brakes, and more particularly to a manual cable operated release apparatus for electrically actuated emergency/parking brakes.
A typical vehicle brake system includes an emergency/park brake apparatus that is used to hold the vehicle in position while it is parked, or to stop the vehicle in the event the primary braking system fails. In some modern vehicles, the emergency/park brake apparatus is normally electrically actuated.
In such an electrically actuated brake apparatus, an electrical drive motor is used during normal emergency and park brake operations to drive a ball screw, or other drive device, to engage the brake. When electrical power is removed from the motor, however, spring forces inherent in the brake apparatus can cause back-driving of the drive device and drive motor, thereby releasing the brake. Vibration increases this inherent tendency.
To ensure that the drive device does not inadvertently back-drive and release the brake, an electrically actuated locking mechanism is incorporated into the drive devices of some electrically actuated brakes. While the addition of the locking mechanism solves the problem of inadvertent back-driving, it creates another problem, in that it may be desirable or necessary in some instances to release the brake under circumstances when electrical power is not available.
What is needed, therefore, is an improved electrically actuated brake apparatus that can be electrically locked against release when power is removed, and having provisions for manually unlocking and releasing the brake apparatus, in those circumstances when electrical power is not available.
Our invention provides a manually operated cable release apparatus, suitable for use in an electrically actuated brake, for a locking mechanism having a shaft that is rotatable about an axis of rotation of the shaft between a first angular position, where the locking mechanism is disengaged, and a second angular position where the locking mechanism is engaged.
In one form of our invention, the cable release apparatus includes a lever having one end thereof fixedly attached to the shaft and extending outward from the shaft for applying a force to the lever, for rotating the shaft back and forth through an angular displacement between the first and second angular positions. A cable is operatively connected to the lever for allowing the shaft to rotate freely back and forth through the angular displacement of the shaft between the first and second angular positions without movement of the cable from a non-engaged position of the cable, and for engaging and applying a tensile force from the cable to the lever for rotating the shaft to the first position from any point in the angular displacement between the first and second angular positions of the shaft.
In another form of our invention, an improved method and apparatus are provided for electrically actuating a brake, in a manner allowing the brake to be selectively electrically locked against release when power is removed, through the use of a locking mechanism in the form of a jaw-tooth clutch operatively installed between the shaft and the housing of a drive motor, for engaging the brake. A manual cable release apparatus is integrated into the brake apparatus for unlocking and releasing the brake, should the drive motor or the power source connected to the drive motor malfunction, or in the event that electrical power is not available for some other reason.
The foregoing and other features and advantages of our invention will become further apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of our invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.